Three major hypotheses will be investigated in interstitial cystitis. Experimental and clinical studies will focus on the interaction between urine and transitional epithelium. Preliminary evidence has indicated that urine from IC patients may contain toxic component(s) not present in normals and that the bladder mucosa has an altered permeability which can be measured clinically in humans and rodents by urea leakage. These two observations may provide a new approach for investigating the etiology of this disorder. A key strength of this proposal is the ability to utilize the large patient base of an established IC investigator (130-150) new patients/year). Clinical specimens from these patients will provide a well controlled source of pathological material (urine, bladder biopsy tissue and serum) for research investigations that will test our hypotheses: 1). Interstitial cystitis patients have a dysfunctional "leaky" epithelium: We shall both improve and utilize our human in vivo measure of epithelial permeability to determine if the glycosaminoglycans (heparin) can restore the bladder "blood-urine barrier" in IC patients. 2). Tissue culture methods can be developed to provide a source of transitional epithelial cells from IC patients for research investigations: We have developed methods to grow IC transitional cells and mucosal explants in culture. These methods will be used to examine the cells and explants for anatomic (EM) and protein markers of differentiation. The effect of IC urine on these findings will be examined and compared to control urines. 3). Urine from IC patients has a cytotoxic component(s): Normal urine does not appear to have in vitro cytotoxicity. We will pursue the abnormality of urine in IC patients that causes epithelial injury and determine whether it is abnormally present in urine, or a normal substance not adequately inactivated by natural urinary defense mechanisms in the IC patients. Both Tamm-Horrrsfall Protein (THP) and glycosaminoglycans (GAG) will be investigated as possible compounds that may inactivate noxious agents (by binding to them). Preliminary data shows that both THP and GAG are capable of such activity.